Field of the Invention
The present invention relates to an automatic transmission for vehicles, and more particularly, to a planetary gear train of an automatic transmission for vehicles capable of improving power delivery performance and fuel efficiency and securing linearity of an inter-stage ratio of a shift stage, by increasing a span of a shift ratio while implementing at least advance 10 speeds with a minimum configuration.
Description of Related Art
Recently, increasing oil prices have caused vehicle manufacturers all over the world to rush into infinite competition. Particularly in the case of engines, manufacturers have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by reducing engine size, etc.
For this purpose, research into reduction of weight and enhancement of fuel efficiency through downsizing has been conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages of an automatic transmission has been conducted.
However, as the number of transmission speed stages of the automatic transmission increases, the number of internal components also increases, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Therefore, to increase the improvement effect of fuel efficiency by multi-staging, i.e., providing multiple speed stages, it is important to develop a planetary gear train which may lead maximum efficiency with a small number of parts.
In connection with this, an 8-speed automatic transmission tends to be implemented in recent and the research and development for a planetary gear train which may implement a shift stage higher than the 8-speed automatic transmission has been actively conducted.
However, the recent 8-speed automatic transmission maintains the span of the shift ratio at a level of 6.5 to 7.5, and therefore has a problem in that the improvement effect of fuel efficiency is not large.
Therefore, when the span of the shift ratio of the 8-speed automatic transmission is maintained at 9.0 or more, the linearity of the inter-stage ratio of the shift stage may not be secured, and as a result the driving efficiency of the engine and the drivability of vehicles are reduced. To cope with this, there is a need to develop a high-efficiency automatic transmission of 9 speeds or more.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.